Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts formed of biocompatible materials (e.g., Dacron or expanded polytetrafluoroethylene (ePTFE) tubing) have been employed to replace or bypass damaged or occluded natural blood vessels.
A graft tube material supported by a framework is known as a stent-graft or endoluminal graft. In general, the use of stents and stent-grafts for treatment or isolation of vascular aneurysms and vessel walls which have been thinned or thickened by disease (endoluminal repair or exclusion) is well known.
Many stents and stent-grafts are “self-expanding”, i.e., inserted into the vascular system in a compressed or contracted state, and permitted to expand upon removal of a restraint to an expanded or natural state. Self-expanding stents and stent-grafts typically employ a wire or tube frame configured (e.g., bent or cut) to provide an outward radial force and employ a suitable elastic material such as stainless steel or nitinol (nickel-titanium). Nitinol may additionally employ shape memory properties. A valve structure can be attached to the frame in some embodiments for use in replacement of a native valve.
The self-expanding stent or self-expanding stent-graft is typically configured in a tubular shape, sized to have a slightly greater diameter than the diameter of the blood vessel in which the stent or stent-graft is intended to be used. In general, rather than inserting it in a traumatic and invasive manner using open surgery, stents and stent-grafts are typically deployed through a less invasive intraluminal delivery, i.e., cutting through the skin to access a lumen or vasculature or percutaneously via successive dilatation, at a convenient (and less traumatic) entry point, and routing the compressed stent or stent-graft in a delivery system through the lumen to the site where the prosthesis is to be deployed.
Intraluminal deployment in one example is effected using a delivery catheter with coaxial inner tube, sometimes called an inner tube, and an outer tube, sometimes called the sheath, arranged for relative axial movement. The stent or stent-graft is compressed and disposed within the distal end of the sheath in front of the inner tube.
The catheter is then maneuvered, typically routed though a vessel (e.g., lumen), until the end of the catheter containing the stent or stent-graft is positioned in the vicinity of the intended treatment site. The inner tube is then held stationary while the sheath of the delivery catheter is withdrawn. The inner tube prevents the stent-graft from moving back as the sheath is withdrawn.
As the sheath is withdrawn, the stent or stent-graft is gradually exposed from its distal end to its proximal end. The exposed portion of the stent or stent-graft radially expands so that at least a portion of the expanded portion is in substantially conforming surface contact with a portion of the interior of the blood vessel wall.
In order to compress the stent or stent-graft to the compressed state, crimping techniques are employed to transition the stent from the expanded state to the compressed state. Current crimping techniques involve several separate steps and various parts to load the stent to the delivery system. These techniques can be time consuming and prone to user error.